Drug-dependent antibodies are a rare by serious cause of hemolytic anemia, but little is know of the nature of the antigens recognized by the drug- dependent antibodies. Precise identification of the antigens recognized by drug-dependent antibodies will lead to a better understanding to mechanisms of antibody formation, better methods to detect drug-dependent antibodies and improved treatment of drug-dependent hemolysis. The purpose of these studies is to use serologic and biochemical techniques to determine the nature of the antigens recognized by drug-dependent antibodies. The antibodies will be tested against red cells treated by proteolytic or glycolytic enzymes to determine if the antigens are located on carbohydrates or proteins. Immunoprecipitation or monoclonal antibody capture assays as be used to more precisely define the molecules identified by the drug-dependent antibodies. To confirm the identity of the epitope, the antibody will be tested against red cells that lack the suspected target molecule. Tolmetin-, cefotetan- and quinine-dependent antibodies will be tested. Initial studies show that reactions of the quinine-dependent antibodies are inhibited by proteolytic enzymes, but those of tolmetin- and cefotetan-dependent antibodies are enhanced.